Sub-sea couplings for high pressure hydraulic lines are well known. Most embodiments comprise a mating pair of couplers, of which the male coupler has a probe which is received in a socket in the female coupler and both couplers contain a self-sealing poppet valve disposed so that when the couplers are mated the poppet valves mutually engage whereby they are lifted off their respective seats and allow hydraulic flow between the couplers.
Very substantial efforts have been made to achieve designs which are efficient and durable, which avoid the ingress of sea water when the couplers are made up or disengaged and which avoid hydraulic lock and which do not require high insertion or separation forces.